1. Field of the Invention
The present invention relates to a sealant used for an ink jet head mounted on an ink jet recording apparatus for recording by ejecting ink to a recording sheet, an ink jet head, and an ink jet recording apparatus.
2. Description of the Related Art
An ink jet head used in an ink jet recording apparatus includes a discharge element substrate on which electrothermal transducers generating energy for discharge are provided. Electric pulses used for driving the electrothermal transducers are applied from the outside using a wiring substrate or the like. The wiring board and the discharge element substrate are electrically connected to each other by inner lead bonding (ILB). Such an electric connection portion is sealed with a sealant or an adhesive in order to prevent corrosion and short-circuiting of electrodes and wiring, which contribute to electric connection, due to mist of the ink filled at the time of discharge.
FIG. 1 shows an example of a configuration of a conventional ink jet head using a sealant or an adhesive for electronic mounting. FIG. 2 is an enlarged sectional view of the vicinity of an electric connection taken along line II-II in the ink jet head shown in FIG. 1. In FIG. 2, reference numerals 121 and 122 each denote a supply port for supplying an ink to a discharge orifice 105. A discharge element substrate 101 includes a discharge orifice 105, an energy generating element (not shown), an electronic circuit element (not shown), and a driving electrode 107 provided on the same surface as the discharge orifice 105. The driving electrode 107 is electrically connected to a connection electrode 108 of the wiring board 102 (hereinafter referred to as a “surface electrode configuration”). In addition, the discharge element substrate 101 is fixed to a support member 103 with an adhesive 131, and the space between the side surface of the discharge element substrate 101 and the support member 103 is sealed with a sealant 110. The connection between the driving electrode 107 and the connection electrode 108 is sealed with sealants 110 and B 111 so as to be protected from an ink. In such a configuration, the sealant is thickly formed for preventing short-circuiting and migration in an electrode portion. When the thickness of the sealant is determined, the shortest distance between the discharge orifice and recording paper is inevitably determined. Since the landing accuracy during ink discharge improves as the distance (paper distance) from the recording paper decreases, a configuration including a thinned sealant has the large problem of securing electric sealing reliability in order to improve print quality. Further, in the use of a recording head, a recording medium or the like may come into contact with a sealing portion due to paper jam. Therefore, a configuration including a sealing portion opposed to a recording medium is required to have mechanical strength.
U.S. Pat. No. 6,123,410 proposes a configuration in which a driving electrode is provided on a surface opposite to a discharge orifice of a discharge element substrate and is electrically connected to a connection electrode formed on a support substrate (hereinafter referred to as a “back electrode configuration”). FIG. 3 is a sectional view of a head configuration disclosed in U.S. Pat. No. 6,123,410. An ink supply port 242 is formed on the back of a surface of a print head 218 where a discharge orifice 238 is formed, and a driving electrode 284 is provided near the ink supply port 242 and is electrically connected, through a solder bump 200, to a connection electrode 285 on a surface of a support substrate 220 on which electric wiring is formed. Further, the solder bump 200 used for mounting the support substrate 220 and the print head 218 is formed in a ring around the ink supply port 242 so as to function as a fluid boundary for the ink supply port 242. The solder functioning as the fluid boundary is corroded with some kinds of ink to form a space in the ring, thereby causing ink penetration into an inner electrode connection portion and an ink leakage. Further, the corrosion of the electric connection may cause defective electric connection. Therefore, there has been disclosed a method for forming a fluid division wall by under-filling a sealant (adhesive) after the connection between both electrodes and the bump.
However, in the above-described configuration, for example, when the bump is formed near the opening of the ink supply port, the sealant which covers the bump is applied so as not to sag and clog the ink supply port, and thus the seal region is narrowed, thereby significantly decreasing the sealant thickness between the sealant and an ink. In this state, the sealant constantly contacts an ink, and thus migration may occur between the electrodes due to ink absorption (water absorption) of the sealant itself. Alternatively, because the bonding area is narrow, the sealant may be scraped due to a reduction in adhesive force, thereby causing a short-circuit. For the above-mentioned reasons, it is very difficult to maintain adhesiveness and electric sealing reliability.
On the other hand, Japanese Patent Laid-Open No. 2002-208652 discloses a sealant containing an oxetane compound. In addition, Japanese Patent Laid-Open No. 2002-302536 discloses an ink jet head using an oxetane compound.
In these documents, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene is exemplified as the oxetane compound. However, the sealant disclosed in Japanese Patent Laid-Open No. 2002-208652 is applied to general electronic devices, and thus the performance in such a severe environment that the sealant contacts an ink is not described. In Japanese Patent Laid-Open No. 2002-302536, ink resistance is evaluated only by a swelling rate, the influence of an eluate of a sealant cured product into an ink is not described, and an acceptance or rejection criteria for evaluating the swelling rate is 5%. A region with a swelling rate lower than this (low water absorption) is not described.
A sealant or adhesive used for an ink jet head contains alkali and polar solvents and has the large problem of maintaining the characteristics described below in a severe environment in which it contacts an ink exhibiting properties which change with color.
(a) Low-Temperature Curability
Since a plurality of different materials is used in constituent members of an ink jet head, low-temperature curability is required for suppressing deterioration in the materials due to heating of curing and warping of the members due to differences in expansion between the different materials.
(b) Bonding Reliability
It is necessary to maintain bonding reliability between the members having different expansion coefficients and composed of a plurality of different materials such as an organic/inorganic material, a noble metal, and the like.
(c) Electric Sealing Reliability
It is necessary to suppress a defective connection caused by corrosion, short-circuiting, or migration accelerated by ink absorption of electrodes and wiring which contribute an electric connection.
Further, an ink jet head with the surface electrode configuration or back electrode configuration has a large problem with bonding reliability and electric sealing reliability in a thinned state required for a sealing material.